Enhance bridge for better target merging

When annotations are loaded/updated in either side, they will be
automatically transmitted to the other side by the bridbe plugin.

Then on the other side, the new data is merged into any existing one.

The problem is that when doing this merge, some fields (which are objects
themselves) should not be overwritten; they should be merged, too.

This change adds selective handling of the `target` field, which is
a list of objects. Now each individual target is merged, ever overwritten.

Furthermore, there are a few special cases when some fields
(inside targets) should not be updated at all.

Now those updates are refused.

Fixes #1198.

h/js/plugin/bridge.coffee

@@ -11,6 +11,75 @@ class Annotator.Plugin.Bridge extends Annotator.Plugin
     'annotationsLoaded': 'annotationsLoaded'
     'enableAnnotating': 'enableAnnotating'
 
+  # Helper method for merging info from a remote target
+  @_mergeTarget: (local, remote, gateway) =>
+#    console.log "Updating target in",
+#      if gateway then "sidebar" else "host frame"
+
+    deleted = []
+    for field, val of local when (not remote[field]?)
+      if not gateway and field in ["diffHTML", "diffCaseOnly"]
+#        console.log "Ignoring attempt to delete", field, "from host frame"
+      else
+        deleted.push
+          field: field
+          value: val
+
+    changed = []
+    for field, val of local when (remote[field]? and remote[field] isnt val)
+      unless Array.isArray val
+        if not gateway and field in ["quote"]
+#          console.log "Ignoring attempt to change", field, "in host frame"
+        else
+          changed.push
+            field: field
+            oldValue: val
+            newValue: remote[field]
+
+    added = []
+    for field, val of remote when (not local[field]?)
+      added.push
+        field: field
+        val: val
+
+    if deleted.length
+#      console.log "Deleted old values:"
+      deleted.forEach (d) ->
+#        console.log "'" + d.field + "': ", d.value
+        delete local[d.field]
+
+
+    if changed.length
+#      console.log "Changed values:"
+      changed.forEach (c) ->
+#        console.log "'" + c.field + "': '" + c.oldValue + "'" + " -> " + "'" + c.newValue + "'"
+        local[c.field] = c.newValue
+
+    if added.length
+#      console.log "Newly added values:"
+      added.forEach (a) ->
+#        console.log "'" + a.field + "': ", a.val
+        local[a.field] = a.val
+
+
+  # Helper method for merging info from a list of remote targets
+  @_mergeTargets: (annotation, remote, gateway) =>
+
+    local = annotation.target  # The current target list
+
+    if local and local.length > remote.length
+      console.log "Ignoring update which would make me loose a target in",
+        if gateway then "sidebar" else "host frame"
+    else if local and local.length is remote.length
+      # Same targets, just update the data
+      for i in [0 ... local.length]
+        @_mergeTarget local[i], remote[i], gateway
+    else
+      # We have more targets now!
+      console.log "Receiving new targets in",
+        if gateway then "sidebar" else "host frame"
+      annotation.target = remote
+
   # Plugin configuration
   options:
 
@@ -40,8 +109,8 @@ class Annotator.Plugin.Bridge extends Annotator.Plugin
     # keys of the remote object into the local copy
     merge: (local, remote) ->
       for k, v of remote
-        if k is "target" and local[k] and local[k].length > v.length
-#          console.log "Ignoring update which would make me loose a target."
+        if k is "target"
+          Bridge._mergeTargets local, v, @gateway
         else
           local[k] = v
       local